Automatic defrosting mechanism



Feb. 8, 1955 T. w. DUNCAN AUTOMATIC DEFROSTING MECHANISM 3 Sheets-Sheet1 Filed Feb. 17. 1950 Ina:

INVENTOR. WWW gfla 1101: n

Feb. 8, 1955 r. w. DUNCAN 2,701,450

' AUTOMATIC DEFROSTING MECHANISM Filed Feb. 17, 1950 :s Sheets-Sheet 2"9 'rnmnoam' 97 83 la? f 94 9:

31/ 1M 1 mtg 5mm i LINE 99 conmzssoa j'm f m '82 umr 67 wncu 88 1047no.|. EVAPORATOR 90 Q conmssson 92 h -26 MOTOR ASSEMBLY swn'cn 9/CABINET ucmr INVENTOR.

Feb. 8, 1955 T. w. DUNCAN 2,701,450

AUTOMATIC DEFROSTING MECHANISM Filed Feb. 17, 1950 3 Sheets-Sheet 3 INVEN TOR.

United States Patent 2,701,450 AUTOMATIC DEFROSTING MECHANISM ThomasWilliam Duncan, Evansville, Ind., assignor to Seeger RefrigeratorCompany, St. Paul, Minn., a corporation of Minnesota ApplicationFebruary 17, 1950, Serial No. 144,641

9 Claims. (Cl. 62-4) .been operated for a predetermined period of time,which depends upon the length of time during which the door has beenopened, as the amount of frost collected on the evaporator is determinedto a large extent by the amount of warm air which is allowed to enterthe cabinet, which is, in turn, governed by'the length of time that thecabinet door is open.

Another object is the'provision of an improved defrosting mechanismwhich is adapted to totalize the length of time during which the door ofa-cabinet of a household refrigerator is open, and upon reaching apredetermined total the mechanism is adapted to accomplish a sequence ofevents which lead to the defrosting of the evaporator and the resettingof the mechanism for totalizing.

Another object -is the provision of an improved defrosting mechanismwhich utilizes an-electric heater, and in which the electric heater ismost efficiently applied so that the defrosting will be accomplishedevenly and completely and there will be no hot spots developed; the

foregoing being accomplished by a maximum refrigerant circulation takingplace in the evaporator when the heat is applied.

Another object is the provision of an improved defrosting system inwhich provision is made for automatic disposal of the water orcondensate resulting from the defrosting, by utilizing the heat of thecondenser and/ or the motor compressor to evaporate the condensate.

Another object is the provision of an improved defrosting system inwhich the length of time between defrosting operations is controlled bythe amount of time the door of the cabinet is permitted to remain open,and in which the same mechanism is totalizing the open time periods ofthe door and is utilized for timing thedefrosting operation.

Another object is the provision of an improved defrosting system inwhich the motor compressor is automatically disconnected or deenergizedduring the defrosting operation, and in which the automatic mechanismmay be overridden at any time by a manual control so that the user onconcluding that defrosting should be accomplished at once, can advancethe cycle manually, or the user can delay the defrosting or extend thelength of period during which defrosting is accomplished, or expeditethe return of the mechanism to its normal operation betwen defrostingperiods.

Another object is the provision of an improved system of the classdescribed, which is simple in construction, certain and positive in itsaction and operation, and which may have its characteristicspredetermined for more humid or less humid conditions, depending uponthe area in which the refrigerator is to be used.

Another object of the invention is the provision of a mechanism whichmaybe manufactured at a low cost, which has a long life, and which maybe operated throughice nection of the heater from the circuit before thetiming device stops so that there will be no possibility of heateroperation without timing control.

Other objects and advantages of the invention will be apparent from thefollowing description and the accompanying drawings, in which similarcharacters of reference indicate similar parts throughout the severalviews.

Referring to the drawings, of which there are three sheets, accompanyingthe specification,

Fig. 1 is a vertical sectional view taken through the cabinet of a.household refrigerator, and showing the evaporator and mechanism inelevation;

Fig. 2 is a diagrammatic plan view of the switch operating mechanism andthe manual control which permits overriding of the automatic control bythe user;

Fig. 3 is a fragmentary sectional view taken on the plane of the line 33of Figure 2, showing the gears and clutch for permitting manual control;

Fig. 4 is a fragmentary sectional view taken on the plane of the line4-4 of Figure 2, looking in the direction of .the arrows, showing thecam and switch mechanism;

Fig. 5 is' an end elevational view of the control knob and the indicatorplate beneath it, seen from the bottom of Figure 2;

Fig. 6 is a schematic wiring diagram of the defrosting system; and

Fig. 7 is a fragmentary view similar to Figure 1, showing a modifiedform of liquid disposal system.

Referring to Fig. 1, 10 indicates in its entirety a householdrefrigerator equipped with a defrosting system embodying my invention.Such a refrigerator comprises a cabinet havingan outer shell 11, aninner liner 12 spaced from the outer shell, and the space between themfilled withinsulation 13.

The cabinet may have a food storage compartment 14 containing anevaporator 15 which serves to cool the food storage compartment 14, andalso serves to provide a freezing compartment which is closed by meansof a cover 16. The cabinet 11 is opened at the front and is closed bymeans of a door 17, and may be provided at its lower end with a machinecompartment 18, which includes a motor compressor 19 and a condenser 20.

The machine compartment 18 has a door 21 at its forward end, and is openat its rear end.

The condenser 20 extends across the currents of air which enter at theopening 22 below the door, and which A pass around the motor compressor19 and out the open back of the machine compartment 18.

The machine compartment 18 has guides 23, which may support a condensateevaporation pan 24.

In the present embodiment of the invention the system includes anelectric heater plate 25 suitably enclosed, and preferably located belowthe bottom of the U-shaped evaporator 15, where it will produce themaximum circulation of the refrigerant in the evaporator and produce adefrosting action, which is even and complete, without hot spots. Theterminals and conductors from the heater are sealed against moisture andvapor to prevent short circuits or grounds.

The heater is preferably of the type in which a resistance wire isenclosed and insulated in refractory covered by a copper tube.

The heater is preferably enclosed in a metal case so constructed thatthe case will be free to drain any moisture that may have accumulatedduring the refrigeration cycle. Aluminum wool or turnings may be packedinto the case of the heater for facilitating the transfer of heat to theevaporator, with which the heater case is in contact, thereby loweringthe operating temperature of the heater.

Below the heater there is a collection system for the condensate, whichincludes a condensate collecting tray 26, which is preferably slightlylarger than the heater and evaporator in bottom plan, so that allmoisture from the latter will drop into the tray 26.

tube 28, which is located to discharge into a funnel 29. The funnel 29communicates with a tube 30, which passes through the wall of thecabinet and has a downwardly extending portion 31 extending down theoutside of the shell. The tube 31 is turned inward at 32, and has itslower discharge end portion 33 so located that it discharges into theevaporating tray 26.

Referring to Fig. 7, this is a modification in which the collectionsystem has its downwardly extendingcom duit in the form. of acorrugation or pressed groove'34 formed in the liner 35. This groove isof sufficient size and such contour that the water will be conducted tothe bottom of the liner'without spreading over the wall of the liner.

At its lower end the liner slopes toward the discharge port 36 over itsentire bottom 37 and over a ledge 38 at the bottom of the groove so thatthe condensate all runs through the discharge opening 36. Thiscommunicates with a conduit 39, which extends downwardly and is turnedlaterally'to discharge into the condensate evaporation tray 24.

In this case the discharge pipe 40 from the collection tray 26 shouldextend over into contact with the wall of the liner in the groove 34,where it preferably points downwardly to facilitate the direction of thecondensate down the groove. tray 24 is preferably surrounded by atubular rubber connector, which is grooved to be received in a hole inthe lower wall of the shell so that it is stably supported by the shellin such position to support the drain line 39.

Thus the water drained from the condensate collection tray duringdefrosting will be conducted to the evaporation tray 24, which isdisposed close to the condenser 20 in each case. The air passing overthe evaporating tray 24 and the heat radiated frfom the condenser 20causes the condensate to evaporate continuously when the motorcompressor is operating; and between these periods it evaporates also,at a slower rate.

The evaporator tray should be conveniently removable for cleaning in theevent foodstuffs have been spilled in the compartment in such way as toenter the evaporating tra y The defrosting of the refrigerator iscontrolled by a defrosting control unit 41 (Fig. 1), which is preferablylocated between the liner 12 and the shell 13 behind the top breakerstrip, with its control knob 42 exposed, but covered by therefrigeratorcover 17.

The mechanism of the defrosting control unit includes a self-startingsynchronous clock motor, indicated at 43 (Fig. 6), the drive shaft 44(Fig. 3) of which is provided with a driving pinion 45. The pinion 45drives a gear 46 (Fig. 2) which is mounted upon hub 47 in a groove 48for free rotation with respect to the hub 47.

The hub 47 is fixedly mounted on the driven shaft 49 and fixedlysupports a spring double acting clutch 50. The clutch 50 comprises aspring spider with a central hole, receiving a reduced part of the hub47, which may be spun over inside the aperture of the spider. The fourspring arms 51 of the clutch bear on the side of the gear 46 and providea friction drive, which drives the gear, but permits manual adjustmentbetween the gear 46 and the shaft 4% The gear 46 reacts against thecollar 52 fixedly carried by the shaft 49. The shaft 49 carries a cam53, which is adjustably mounted on the shaft by means of a hub 54 and aset screw 55. The cam 53 has a partially circular part 56 of reducedradius corresponding to the frosting time, and a partially circularportion 57 corresponding to the defrosting period. These two circularparts of the cam are joined by two straight portions 58 and 59,comprising the rise and the drop of the cam.

The circular portions 56 and 57 serve as the dwell parts of the cam,during which the control switches are held in predetermined position.The shaft 49 extends forwardly out of the housing of the defrostingcontrol unit 41 through a dial plate 60, which may be provided with theindicia Defrost Control. It may also have a circular scale with scaledivisions, indicating the frosting period and the defrosting period, andalso an arrow indicating the direction of rotation.

The knob 42 is preferably provided with a pointer or arrow 61, whichindicates the position of the cam with respect to the dial plate 60, andshows whether the refrigerator is frosting or defrosting.

the spring actuated snap switch type.

The drain pipe 39 to the evaporator When the system is operating and itis found that unusual conditions have'made a efrostm cycle necessary,but the knob has not arrived at the de rosting point, the knob can thenbe turned manually to the index point 62 for defrosting; and thedefrosting cycle will automatically start and be automaticallycontrolled to completion because the cam 53 turns with the knob 42 andthe shaft 49.

If it is found that a defrosting cycle was incomplete because of aninitially heavy frost build-up, the knob can be turned to the indexpoint for defrosting, which is permitted by'means of the double actingclutch and the entire defrosting cycle, or any portion ofthe cycle, canbe repeated.

If it is found that the knob indicates a defrosting cycle is about totake place, whereas conditions indicate that defrostin is not yetnecessary, knob 42 may be turned backwar delaying the defrosting as muchas desired.

The same plate may serve both for the defrosting knob and the thermostatadjustment knob (not shown).

The cam 53 actuates a pair of switches, preferably of Such switchesinclude actuatingbuttons 63 and 64, the switches being mounted in asingle housing 65 provided with connectors 66 and 67. Such'snap switchesof the toggle type require a predetermined motion of the actuatingbutton before they snap from open to closed position, or vice versa, andalso permit further motion after they have been actuated, withoutaffecting the switch.

They may be of the type that includes a pair of springs. one forproducing the snap action, and the other for urging the switch into ahome position; that is, with both actuating buttons 63, 64 outward.

The presentsystem preferably utilizes switches which permit a time lagbetween the two switches 63 and 64; and the snap switches just describedhave this characteristic, of which I prefer to take advantage, forreasons further to be described.

The cam 53 may act upon a follower 68 (Fig. 4) which is fixedly securedupon a pin 69 by means of a circular portion 70. The follower 68 has itsend curved outwardly from the cam at 71 so that it will ride upon thecam freely in either direction. The pin 69 is mounted upon bearings (notshown), and also carries a switch actuating arm 72 fixedly secured topin 69. The switch actuated arm 72 extends radially, and has a laterallybent end portion 73 forming an actuating flange.

This actuating flange engages separate leaf sprin s 74. 75 for the twoswitches 63, 64. The leaf springs 4, 75 are fixedly secured to theswitch unit 65 at their upper end by means of a screw or screw bolt 76.The actual ing flange 72 is cut away at 77 over that portion of it endWhlCh engages the leaf spring 75, but it projccv. farther toward theleaf spring 74.

This means that the actuating flange 72 will come into engagement withthe leaf spring 74' first, and will actuate switch 63 first; and uponbeing moved farther, during' the rise 58 of the cam, the actuatingflange 72 will have its edge 77 brought into engagement with the leafspring 75; and will then actuate the switch 64.

T1118 means that. upon clockwise rotation of the cam 53 switch 63 willbe actuated first; and after a slight time lag switch will be actuatednext. Upon the discharge of the follower 68 down the sloping surface 59of the cam 53, a reverse action will take place; and switch 64 will bepermitted to move to its former position first; and after apredetermined time lag'switch 63 will move back to its initial osition.

The reason for t is time lag will be further explained after thedescription of the operating circuit. The operating circuit is showndiagrammatically in Fig. 6, in which the synchronous clock motor hasalready been indicated by the number 43. The control switches arc shownin the approximate position which. they assume durin the defrosting; andthe movable switch arms have been indicated by the numbers 63 and 64.

The present system is intended to be energized by a 110 volt, 60 cyclesource of lighting current. The switch arms 63, 64 are seen below thedouble throw switches; and the fixed contacts of these switches havebeen indicated by'numbers 78-81. The terminals of the clock motor 43 areconnected to the moving switch arms 63, 64; but the moving switch arm 64is also connected by a conductor 82 to the line conductor 83. The otherline conductor 84 is connected by a conductor 85 to the moving contactarm 86 of a synchronous clock motor 43 is energized only when the I doorswitch is closed; and that 1s, when the door s opened and the light 91is illuminated.

The purpose of this is to control the operation of the clock motorresponsive to the opening of the door. In this manner the running of theclock motor 43 totalrzes the time during which the door is open.

A desirable total'in terms of frost build-up can be determinedexperimentally, taking into consideration the most severe humidityconditions to be encountered in the field. Thus, when the switch 63 isinns left hand position, the clock motor is adapted to totalize the timeduring which the door is open and to express this total by means ofreducing gears in the rotative movement of the cam 53.

The amount of the periphery which is devoted to the circular part 56indicates the time which. has been determined experimentally for abuild-up of frost on the evaporator; and when the cam has rotated anamount equivalent to the peripheral portion 56, the evaporator willordinarily have arrived at a condition when defrosting is desirable.

The other position 79 for the switch 63 connects the clock motordirectly to the line throu h the conductors 88 and 85 so that the clockmotor is. ta en from the control of the door switch; and the clock motormay now be used for timing the on period of an evaporator heater 25 inthe form of an electric heating element, previously described. a

The compressor motor of the motor compressor unit 19 is preferably ofthe induction type, which does not interfere with radio receivingcircuits; and its three energizing conductors 94-96 extend to a motorstarting relay 97, one terminal of which 1s connected byconductor 98 tothe line conductor 84.

The other terminal of the motor starting relay is connected by theconductor 99 to the fixed contact 100 of a thermostatic switch unit 101.The movable contact 102 of the thermostatic switch unit is connected byconductor 103 to the fixed contact 80 of switch 84, which s the leftcontact. The fixed contact 81 of switch 64 is connected by conductor 104to one term nal of the electric heating element 25. The other terminalof the electric heating element 25 is connected by conductor 105 to lineconductor 84.

This means that when the switch 64 IS in the left hand position,engaging contact 80, the motor compressor unit is energized undercontrol of the thermostatic switch 101 so that refrigeration may proceedin the normal manner. When the switch 64 is in the right hand position,engaging contact 81, the motor compressor unit is de-energized, eventhough the thermostatic switch may close, because it is not desirable tooperate the motor compressor at the same time as the evaporator heater.

In this, the right hand position of the switch 64, engaging contact 81,evaporator heater 25 1s energized through conductors 82, 104, and 105.Thus the left hand position of both switches corresponds to the normaloperation of the refrigerator and the frosting period,

. during which the clock motor totalizes the amount of door opening; andthe movement of the cam depends upon the amount of time the door remainsopen.

The right hand position of both switches corresponds to the defrostingcycle, during which the clock motor is not controlled by the doorswitch, but continues to operate and to move the cam through thatportion of the cycle corresponding to the evaporator defrosting.

The two switches 63 and 64 are preferably operated with such a time lagthat switch 63 is moved tothe right first, and switch 64 is moved to theright second, after a time lag, as previously described.

Switch 64 is the first to move to the left 111 Flg. 6; and after a timelag, switch 63 moves to the left for safety and to make sure that thereis no possibility of the clock motor stopping and remaining still whilethe heater operates.

This tune lag need only consist of a few seconds, such as, for. example,fifteen to thirty seconds; and tive assurance that the clock will not bestopped by the opening of the door switch after the heater element hasbeen turned on. For example, suppose the last door opening prior to adefrosting period is still going on at the time when the cam arrives atthe defrosting period. If the switches were actuated simultaneously, thecam might then turn on the evaporator heater'before the actuation of theswitch 63 to disconnect the clock from the control of the door switch.

Manufacturing inaccuracies might permit this to happen, leaving theheater operating and the clock motor under the control of the doorswitch for a very short time. .Under these conditions, when the door isclosed, the door switch would open, stopping the clock motor and alsostopping the rotation of the cam. The heater would be operating; but theclock motor would not be timing the heating period.

If the mechanism should ever arrive at this position. the operation ofthe clock motor would be stopped; and the cam would not act further toclose the contacts 63 and 79. The heater would then remain on until thenext cabinet door opening; andv if there were no time lag between theswitches, at that time, upon opening of the door the clock motor wouldbe energized through contacts 63, 78, and another timed defrosting wouldprobably take place, in addition to the time during which the door wasclosed and the heater operated without being timed.

There should be no possibility of the heater operating without beingtimed because of the damage which might occur'from too much heat; andtherefore the switches preferably operate with a definite time lagbetween them so that by having the switch 63 operate before the heateris turned on, the timing motor is always running and ready to controlthe heater first; and by having the heater cut off first, by means ofthe switch 64, while the timer is still operating, positive control ofthe heater and timing of its operations is always assured.

The operation of the automatic defrosting system is as follows:Ordinarily both the switches 63 and 64 will be in their left handposition, during the normal operation of the refrigerator; and theevaporator heater will be turned off, and the timing motor will be underthe control of the door switch.

The motor compressor unit operates in the usual way, being controlled bythe thermostatic switch, to compress refrigerant and supply refrigerantto the evaporator only when the temperature rises above a predeterminedlimit the following reason. It is very desirable for the timing deviceto be running before the heater is turned on and desirable for theheater to be turned 0E before the timing device is stopped, both fromthe point of view of at the point where the thermostat is located,whether it be inside the evaporator 15 or on the outside, or in thestorage chamber 14.

While the door of the refrigerator is closed, the evaporator 15, beingoperated at a point below freezing, it i will cause the vapor in the airto condense upon its surface in the form of frost, tending to dehydratethe air in the refrigerator, during the cooling operation. Whenever thedoor is opened new air gains access to the compartment 14 and to theevaporator 15; and this air contains an amount of moisture, dependingupon the humidity conditions at the point where the domesticrefrigerator is being used. The amount of frost accumulated depends.upon the length of time the door remains open.

As the clock motor is a self-starting synchronous motor, it will runduring the periods of time that the door is open, and will totalize thetime during which the door is open by rotating the cam 53 through thereduction gears over a predetermined amount.

When the cam 53 has been rotated to the point where the riser 58 engagesthe follower 68, switch 63 will be moved to the right, first closing thecircuit to the clock motor directly to line, and taking the clock motorout of control of the door switch. The clock motor then continues tooperate; and a few seconds later the cam 53, having been rotatedfurther, the riser 58, actuating the follower 68, moves the flange 72 tosuch a point that the edge 77 engages the switch 64 and moves it towardtheright hand position of Fig. 6.

The breaking of the circuit at 64, 80 takes the motor compressor unitcompletely out of circuit and connects the evaporator heater in circuit.Refrigeration then it is posiceases; and the heating of the evaporatorto defrost the evaporator commences.

The electric heater attached to the evaporator raises the temperature ofthe parts of the evaporator and the refrigerant inside it. Therefrigerant rises in the conduits and tends to warm up the entireevaporator. 'The location of the heater or heaters should be selected togive a maximum circulation of the refrigerant. The

heater is kept on during the periodwhen the circular part 57 of the campasses over the follower 68.

The length of this part of the cam IS experimentally determined for thelocality in which the refrigerator IS to be used, and is sufficient topermit the complete deare still operating, but refrigeration commencesand the timing of the heating period continues for a short time duringthe time lag between the switches.

As the follower 68 passes down the inclined portion 59 of the cam to thecurved portion 56 of lesser radius, the follower is permitted to move insuch manner that the actuator 72 recedes from the switch button 63; andthe switch 63 moves from the right hand position to the left handposition in Fig. 6. This cuts the timing motor off the line at thecontact 79 and puts it under the control of the door switch 86 again.

Of course, if the door happens to be open at that moment, the timingmotor would continue to operate and to rotate the cam until the door isclosed.

Thereafter the frosting period takes place again;'and the clock motortotalizes the periods of time during which the door is open and duringwhich frost is being accumulated again.

In the event that the user of the refrigerator wishes to advance thecycle to have the defrosting take place at once, he need only turn theknob 42 in the clockwise direction around to the defrosting indicator62; and defrosting will take place at once because this will move thecam to the proper position to actuate the switches.

In the event the user does not wish to defrost yet, he may turn the knob52 backward and may let the refrigerator accumulate frost again for aslong a period as he may desire.

If the defrosting has not been complete, the user may again turn thecontrol knob to the defrosting position, all of this being permitted bythe clutch 50, which slips with respect to the gear 46.

The condensate which is melted from the evaporator is collected by thepan 26 and conducted by the conduit 31 to the evaporation pan 24adjacent the condenser in the machine compartment 18.

As the condenser becomes heated and the motor compressor generates heat,the air passing over the evaporation pan 24 will carry away thecondensate in the form of vapor; and thus the present system isadaptedto dispose of the condensate resulting from the defrosting.

It will thus be observed that I have invented an automatic defrostingmechanism which includes an electric heater for accomplishing thedefrosting, a control unit for initiating and controlling'the defrostingcycle, dependent upon the length of time the door remains open, a systemof collecting the condensate resulting from defrosting, and a disposalsystem to eliminate the water which is so collected.

The present system is flexible and may be overridden by manual controlsso that it is capable of receiving and responding to such attention asthe user desires to give it; but if not given attention, willnevertheless operate automatically.

While I have illustrated a preferred embodiment of my invention, manymodifications may be made without departing from the spirit of theinvention, and I do not wish to be limited to the precise details ofconstruction set forth, but desire to avail myself of all changes withinthe scope of the appended claims.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent of the United States, is:

1. In a refrigeration apparatus having an insulated cabinet having adooropening, a door for closing'the opening, an evaporator, a condenserand a motor compressor, the evaporator being operably connected with tooperate said timer for the duration of time the door is open and meansactuated by said timer after a predetermined time that the door is openfor initiating defrosting of the evaporator by the source of heat.

2. In an automatic defrosting mechanism, the combination of an insulatedcabinet having a door opening and a door, an evaporator in said cabinetfor cooling the space therein, a motor compressor'and condenserconnected with said evaporator, an electric heater in heat transmittingcontact with a part of said evaporator, a door switch adapted to beclosed when the door is opened, and a timing mechanism comprising a synchronous timing motor, a shaft driven by said motor and a cam carried bysaid shaft, a driving clutch connection between the said shaft and saidtiming motor, an indicating knob carried by said shaft and havingindicia for indicating the beginning and end of a defrosting period andthe beginning and end of cooling operations, said shaft being rotatablerelative to said timing motor by said indicating knob for the purpose ofadvancing or retarding or predetermining the time of defrosting orcooling operations, said timing motor being controlled by said doorswitch and energized during cooling operation by the opening of the doorto totalize the time of door opening, during which the evaporator issubjected to increased frosting from the moisture in the air enteringthrough the door opening, the said cam having a dwell of one radius ofpredetermined peripheral length corresponding to the total time of dooropening during which frost may be permitted to accumulate, and the saidcam having a dwell of another radius having a peripheral lengthcorresponding to the length of time during which it is desired tooperate the electric heater for heating the refrigerant in theevaporatorand thereby melting the frost from the evaporator, switchingmeans controlled by said cam for opening the motor compressor circuitand for closing the heater circuit at the beginning of a defrostingperiod, said switching means also disconnecting the timer motor from thedoor switch and placing the control of the timer motor in parallel withthe heating element, the said switching means also reestablishing themotor compressor circuit and the door switch control-of the timer motorand interrupting the heater circuit at the end of a defrosting period,the-switching means being provided with a time lag action between themaking of the parallel circuit for the timer motor and the breaking ofthe door switch circuit so that the timer motor will be in condition tooperate at all times to advance the cam through its respective periodsof cooling operations and defrosting operation without possibility ofstoppage of the timing motor by switching operations.

3. In a refrigerator, the combination of a cabinet with a door. anevaporator, a motor compressor, and a condenser, a door switch havingcontacts which are closed when the door is open. a synchronous clockmotor controlled by said door switch and operated to run when the dooris open. a mechanical device operated by said clock motor and arrangedto operate a first electric switch when the door has been open over apredetermined amount of time, said first switch disconnecting the clockmotor from the control of the'door switch and connecting the clock motorto line, a second switch actuated by said device, and an electric heaterin proximity to the evaporator. said second switch connecting theelectric heater with the line and disconnecting the motor compressorfrom energization so that the refrigerator will not operate while theheater is defrosting the evaporator.

4. In a refrigerator, the combination of a cabinet with a door, anevaporator, a motor compressor, and a condenser, a door switch havingcontacts which are closed when the door is open, a synchronous clockmotor controlled by said door switch and operated to run when the dooris open, a mechanical device operated by said clock motor and arrangedto operate a first electric switch when the door has been open over apredetermined amount of time, said first switch disconnecting the clockmotor from the control of the door switch and connecting the clock motorto line, a second switch actuated by said device, and an electric heaterin proximity to the evaporator, said second switch connecting theelectric heater with the line and disconnecting the motor compressorfrom energization so that the refrigerator will not operate while theheater is defrosting the evaporator, said mechanism including anactuator for said first and second switches, which operates the switcheswith a time lag between them to assure the constant connection of thesynchronous clock motor in circuit so that the operation of the heaterwill be timed whenever it is connected in circuit.

5. In a refrigerator, the combination of a cabinet with a door, anevaporator, a motor compressor, and a condenser, a door switch havingcontacts which are closed when the door is open, a synchronous clockmotor controlled by said door switch and operated to run when the dooris open, a mechanical device operated by said clock motor and arrangedto operate a first electric switch when the door has been open over apredetermined amount of time, said first switch disconnecting the clockmotor from the control of the door switch and connecting the clock motorto line, a second switch actuated by said device, and an electric heaterin proximity to the evaporator, said second switch connecting theelectric heater with the line and disconnecting the motor compressorfrom energization so that the refrigerator will not operate while theheater is defrosting the evaporator, said device comprising a cam and afollower, and said cam having two dwell portions of different radius,one of which corresponds to the frosting period, and the other of whichcorresponds to the defrosting period.

6. In a refrigerator, the combination of a cabinet with a door, anevaporator, a motor compressor, and a condenser, a door switch havingcontacts which are closed when the door is open, a synchronous clockmotor controlled by said door switch and operated to run when the dooris open, a mechanical device operated by said clock motor and arrangedto operate a first electric switch when the door has been open over apredetermined amount of time, said first switch disconnecting the clockmotor from the control of the door switch and connecting the clock motorto line, a second switch actuated by said device, and an electric heaterin proximity to the evaporator, said .second switch connecting theelectric heater with the lin and disconnecting the motor compressor fromenergiz.ztion so that the refrigerator will not operate while the heateris defrosting the evaporator, and a friction clutch interposed betweensaid devices and said clock motor, and having a manual actuating memberso that the frosti or defrosting may be advanced or retarded by usingsaiJ clutch to control frosting or defrosting at will.

7. Refrigerating apparatus of the type having a heatabsorbing unitconnected in a closed circuit with a heat-dissipating unit and in whichthe heat-absorbing u is disposed within an insulated space from whichheat is to be removed, said apparatus comprising a mechanism forcontrolling operation of said apparatus in accordance with thetemperature of said space, a heat source for causing the temperature ofsaid heat-absorbing unit to raised to a degree sufiicient to melt anyfrost which may have collected thereon, a movable door for providingaccess to said insulated space, timing means operable in response to thetotal elapsed time during which said door has been opened for initiatingoperation of said heat source and for restoring the system to thecontrol of the normal operation control mechanism.

8. An automatic defroster system for refrigerator evaporators,comprising a source of electric current, a refrigerator door switcharranged to be closed by open ing the door and opened when the door isclosed, an electric timer motor, conductors connecting said source,motor and door switch, the timer motor operating when the door is opento integrate the total door-open time, an electric heater for heatingrefrigerant in the evaporator to defrost the latter, a reduction gearand cam driven through said gear by said timer motor, a heater switchcontrolled by said cam, to be closed after the timer motor has run apredetermined time, and conductors connecting said source, heater andheater switch, to energize said heater to initiate defrost after thedoor has been open a predetermined total time, which results in thefrosting of the evaporator sufficiently to require defrost.

9. In an automatic defrosting refrigerator,'the combination of aninsulated cabinet, having a door opening and a food storage space, aninsulated door movably mounted on said cabinet, to open or close saiddoor opening, a door seal maintaining an air-tight joint between saiddoor and cabinet, a door switch arranged to be closed by opening thedoor and opened when the door is closed, a timing motor connected to becontrolled by said door switch to operate when the door is open, tointegrate the times when the door is open and the food storage space ofthe cabinet is open to damp external air, an evaporator in the cabinetoperated at a temperature below freezing point of water to cool the airand contents of the cabinet, the said evaporator gathering an amount offrost from moisture in the air, dependent on the total time the door isopen, a motor compressor and a condenser outside the food storage space,connected by conduits in closed circuits with said evaporator, a thermalswitch controlling said motor compressor, responsive to evaporatortemperature, to supply the evaporator with cooling refrigerant, when theevaporator temperature rises above a predetermined degree, an electricheater for heating refrigerant in the evaporator and to cause the hotrefrigerant to be circulated in said evaporator, to melt the frost fromsaid evaporator, and electric switch means controlling said heater andclosed by said timing motor, after said door open periods have amountedto a predetermined total time, to initiate the defrost of saidevaporator.

References Cited in the file of this patent UNITED STATES PATENTS1,701,399 Vickery Feb. 5, 1929 1,913,433 Doble, Jr June 13, 19332,100,284 Kriechbaum Nov. 23, 1937 2,106,042 Stark Jan. 18, 19382,167,442 Alsing July 25, 1939 2,178,807 Ploeger Nov. 7, 1939 2,230,191Knight Jan. 28, 194! 2.299,l74 Plummer Oct. 20, 1942 2.313,390 NewtonMar. 9, 1943 2,324,309 McCloy July 13, 1943 2,400,168 Roach May 14, 19462,463,027 Frie Mar. 1, 1949 2,465,516 Colyer et al. Mar. 29, 19492,492,397 Peterson Dec. 27, 1949 2,522,199 Shreve Sept. 12, 19502,540,723 Geldhot'f et. al. Feb. 6, 1951

